A dealer replaced the leaking fuel tank on my 1974 145 under a safety service campaign. The new tank is a 240 series, 1978 model with a pre-pump in the tank. When I got the car back the original, external fuel pump was making an odd noise : sort of a repetitious qwik-chik, qwik-chik. I took the car back to the dealer. A mechanic said that the noise didn't sound right. But they didn't want to work on the car then. Later I took the car back but it wasn't making the noise and the mechanic only offered that my external pump is no good. No explanation of why it became no good after the tank was replaced. The sound came back but it is now more of a continuous chik-chik-chik noise. The noise is easy to hear standing next to the car.

My only theory is that air is getting trapped in the pump. With the original tank, and with the new one, there seems to be a venting problem. When I fill the tank it is necessary to use a very slow rate of delivery. Also, when I have just filled the tank, the engine will intermittently hesitate as though it is not getting gas. This goes away after some miles or after the car sits. Could a venting problem result in air in the pump and noise from the pump ?

There aren't any performance problems so I could ignore the noise but maybe the noise indicates a failure to come. If I proactively replace the pump should I get a 140 model or is the 240 model preferable since it was designed to work with the pre-pump in the tank ?

Thank you.